The present invention relates to the production of a polymer blend by mixing a thermoplastic organic polymer and an organopolysiloxane at a temperature above the melting point of the thermoplastic organic polymer. Such a melt blending process can be used to produce a polymer blend in which the organopolysiloxane is dispersed in a matrix of the thermoplastic organic polymer. The polymer blend is useful particularly as a masterbatch which can be mixed with further thermoplastic organic polymer to produce an organic polymer composition containing a minor proportion of organopolysiloxane. A masterbatch is usually formed by adding an organopolysiloxane in liquid form to a thermoplastic organic polymer in liquid form, intimately mixing the components in liquid phase, and cooling the mixture to form the masterbatch in solid form. The masterbatch is often in the form of handy powder or pellets.
Thermoplastic organic polymers can be processed for example by compounding or by moulding, for example extrusion or injection moulding, to produce wires, cables, films, fibres or moulded structures such as interior automobile parts. Dispersing a polysiloxane composition throughout the structure of a thermoplastic organic polymer by a masterbatch technique has been proposed for example in U.S. Pat. No. 5,844,031. The polysiloxane can improve the properties of the thermoplastic organic polymer, for example it can reduce its coefficient of friction, increase its hydrophobicity and/or increase its abrasion resistance, scratch resistance and wear resistance.
CN1428370 describes a composition including (wt %) 85-95% of ultrahigh molecular weight polyethylene, 3-15% of polysiloxane and 0.2-2% of antioxidant. CN102153831 describes an acrylonitrile-chlorinated polyethylene-styrene resin composite comprising acrylonitrile-chlorinated polyethylene-styrene grafting powder, styrene acrylonitrile resin, weather-resistance master grain, lubricating agent, antioxidant and heat stabilizer.
JP2001-335691 describes a resin composition containing a low molecular weight silicone resin having molecular weight of 1,000 to 50,000, a high molecular weight silicone resin having molecular weight of 200,000 to a million, and a higher fatty acid amide. JP 2001335691 describes a composition prepared by blending (A) a silicone resin with molecular weight 10,000-40,000 (B) a silicone resin with molecular weight 300,000-500,000 (C) oleamide, (D) polyolefin resin e.g. low-density polyethylene resin and optional additives (e.g. antioxidant, flame retardant, pigment).
US2003/0212159 describes a foamable polymer composition that may contain one or more additives for example inorganic fillers, antioxidants, colorants, pigments, light stabilizers, optical whitening agents, acid scavengers, ultraviolet absorbers, plasticizers, processing aids, ignition resistant additives, viscosity modifiers, antistatic additives or extrusion aids.
To get full benefits of the silicone masterbatch, one needs to get a very fine, homogeneous dispersion of the organopolysiloxane in a matrix of the thermoplastic organic polymer to ensure a long shelf life of this composition made out of two incompatible polymers. This requires thorough mixing of the thermoplastic organic polymer and the organopolysiloxane under high shear at a temperature at which both the thermoplastic organic polymer and the organopolysiloxane are in liquid phases when forming the masterbatch. When organopolysiloxane dispersion is not well controlled, it results in inconsistent performances when the masterbatch is compounded into a thermoplastic organic polymer matrix. For example it may result in forming gels during extrusion, high variation in friction coefficients, delamination or organopolysiloxane transferring from one surface to another during film production. It may also result in low and variable scratch resistance properties when injection moulding plastic parts.
A siloxane or polysiloxane or organopolysiloxane or silicone is a silicon containing compound containing repeating Si—O—Si bonds. Such repeating Si—O—Si bonds form a polymeric chain. The organopolysiloxane has pendant groups which are chemical groups located on the Si atoms along the polymeric chain. The organopolysiloxane comprises terminal groups. A terminal group is a chemical group located on an Si atom which is at an end of the polymer chain.
An organopolysiloxane can be an organopolysiloxane comprising at least one of the following units: M unit (mono-functional), D unit (di-functional), T unit (tri-functional), Q unit (tetra-functional). A M unit has the formula R3SiO1/2 wherein R is a substituent, preferably an organic substituent and each R can be the same or different on a single Si atom. A D unit has the formula R2SiO2/2 wherein R is a substituent, preferably an organic substituent and each R can be the same or different on a single Si atom. A Q unit has the formula SiO4/2. A T unit has the formula RSiO3/2, wherein R is a substituent, preferably an organic substituent. Each substituent R can be selected for example from alkyl, aryl, alkenyl, acrylate, methacrylate and others. For example it can be an alkenyl group having 1 to 6 carbon atoms, for example a vinyl group or a hexenyl group.
A branched organopolysiloxane typically contains at least one T unit and/or at least one Q unit. A linear organopolysiloxane typically contains D units and optionally M units. A polymer is a compound containing repeating units which units typically form at least one polymeric chain. A polymer is called an organic polymer when the repeating units contain carbon atoms. An organic polymer is called a thermoplastic organic polymer when it becomes liquid when it is heated.
We have found that minor changes in the processing conditions used in the preparation of the masterbatch can affect the molecular structure of the organopolysiloxane. This can in turn affect the properties of a thermoplastic organic polymer composition into which the masterbatch is compounded. There is a need for a process in which the molecular structure of the organopolysiloxane is unchanged during masterbatch production, or is less sensitive to variations in processing conditions during masterbatch production.